This invention relates to a novel dicyclopentadiene (hereinafter referred to as DCPD) polymer into which a plasticizer has been incorporated. In particular, it relates to the addition of an ester plasticizer having a solubility parameter from 7.8 to about 10.2 (cal/cc).sup.1/2 to a thermoset poly(DCPD) which is formed via a metathesis-catalyst system. In a preferred embodiment the polymer is formed when two solutions, at least one of which contains plasticizer, one a catalyst/monomer solution and the other an activator/monomer solution, are combined in a reaction injection molding machine and then injected into a mold where polymerization rapidly occurs.
Poly(DCPD) is a crosslinked polymer well suited in a wide variety of applications. One of the great advantages offered by poly(DCPD) is that it can be used to form products via reaction injection molding (hereinafter referred to as RIM).
Reaction injection molding is a process for in-mold polymerization which involves the mixing of two or more low viscosity reactive streams. The combined streams are then injected into a mold where they quickly set up into a solid infusible mass. RIM is especially suited for molding large intricate objects rapidly and in low cost equipment. Because the process requires only low pressures, the molds are inexpensive and easily changed. Furthermore, since the initial materials have low viscosity, massive extruders and molds are not necessary and energy requirements are minimal compared to the injection molding or compression molding commonly used. For a RIM system to be of use in forming a plasticized polymer, the plasticizer must be added before the material sets up. Therefore, it is critical that the plasticizer not interfere with the polymerization reaction.
The advantage of adding plasticizers to poly(DCPD) is a modification of the polymer's physical properties. Numerous applications of poly(DCPD), e.g. highly impact resistant fascia and bumpers for automobiles, require a softer, more elastic material, having a higher impact resistance and greater flexibility than is obtainable with the unmodified polymer. To obtain the physical properties required for these applications a plasticizer must be added.
Unexpectedly, it has been found that ester plasticizers having a solubility parameter of about 7.8 to about 10.2 (cal/cc).sup.1/2 provide improved impact resistance and flexibility. It is surprising that the presence of esters does not prevent the polymerization of dicyclopentadiene, especially where the esters are present at high levels, e.g. up to about 55% by volume of DCPD monomer. In contrast, polymerization is retarded by other materials containing polar functionalities such as alcohols, ethers, ketones and acids. For alcohols and acids, in particular, the amounts that can be tolerated in the polymerization of DCPD is on the order of only parts per million.
Another unexpected feature of ester plasticizers is that they are retained in the polymer network, even at high levels, whereas hydrocarbon oils at high levels show obvious signs of exuding out. One might have expected a hydrocarbon polymer such as poly(DCPD) to have a greater affinity for hydrocarbon plasticizers than for esters, but this is not the case.